Some machines, such as asphalt pavers and log loaders, comprise one or more driving and actuating systems where the operation, particularly speed and direction (e.g., forward and reverse, left and right, in and out, up and down), of each driving and actuating system is separately controlled. Each driving or actuating system often comprises a hydraulic pump for driving—either directly or through a valve—a motor, cylinder or actuator that is coupled to a crawler, wheel(s), linkage(s) or rotating platform. In other cases the driving and actuating systems include an electric motor, the application of electric power to which is controlled by means of switches.
Such machines thus have speed controllers; in some cases, there is a separate speed controller—e.g. a joystick—for different functions of the machine; in other cases, one controller determines the forward speed of the machine, and another determines the deviation from straight-ahead, i.e. the desired angular speed or rate of yaw. The latter may be, for example, a steering wheel or a knob. In yet other cases machines, such as knuckle-boom log loaders, use resolved motion control whereby one controller determines the horizontal speed of an end effector, such as a grapple or bucket, and another determines its vertical speed. The speed commands for each driving and actuating system of the machine are derived from these controllers.
When a hydraulic component malfunctions, e.g. because a swash-plate or spool gets stuck in the open position, or because a switch is welded shut by arcing, it is possible for the hydraulic or electric component to keep applying power to an actuator, crawler or wheel, even when electric power to the control element of said component is turned off.
Devices exist, for example in cars, which detect a machine skidding or rotating uncontrollably, and then modulate power to a wheel or wheels to counteract the problem. They are known, for example, by names such as anti-lock brakes (ABS), electronic-stability programs (ESP) and traction-control systems. These devices deal with problems of machine inertia and/or lack of friction between the machine tires and the ground. They rely on the machine systems being functional, so that the system controller may use the brakes, for example, to alleviate or solve the problem. Thus they do not address the problem of a component failure.
Other devices exist that detect a motion that is forbidden and react to it, such as heater-fans that are shut down when the unit tips over. Thus they do not distinguish between motion that is permissible in one context but not another.
Yet other devices detect a problem in a machine, such as the engine oil pressure being too low, and then shut the engine down. These react to the internal behaviour of the machine, rather than to the machine's behavior in its environment.
It is thus desired to have a machine loss-of-control detection and shutdown system that addresses one or more of these shortcomings. A solution that is reliable, easy to implement, and relatively inexpensive is highly desired.